Explanation of divisions by latitude:

Northern and Southern Russia are separated by latitude 55˚ N

• The latitude 55 degrees North separates the Steppe from the Tundra and I think this is the logical line to use.  The great grassy steppe between 45 and 55 N latitude was a prehistoric interstate highway between east Asia and Western Europe and Scandinavia. Travelers turned either north or south from the Steppe to settle and develop their cultures.

Northern and Southern India are separated by latitude 15˚ N

• India presents some interesting considerations.  Latitude 15˚ N makes sense for two reasons.  The main one is that migration is thought to have followed the coast around the Arabian Pen and then down the west side of India.  As the migrants passed the great N/S mountain range separating modern day Pakistan and Afghanistan, they would have come to the Indus River valley at about 15˚ N Latitude. Some may have been tempted to turn N there.  Also north of this parallel is all of the mountainous little provinces and countries at the edge of the Himalayas.  These is a strong weaving tradition in those mountains that is likely to be different from the rest of India.  However, it may be related to weaving in the Indus Valley so this will keep those areas together.

Northern and Southern China are separated by latitude 30˚ N

• For China, the logical divider is the Yangtze River.  It covers 11 lines of latitude but the lower reaches are the most important for sandal culture. The30 degrees North latitude line enters just  at the south edge of the Tibetan Plateau and in East China comes just below the mouth of the Yangtze which is Shanghai.  In Chinese tradition, the land south of the River is called the Land of Fish and Rice.  North of the River, wheat replaces rice and  pork and chicken in place of fish,so there are distinguishable cultures, at least cuisines.

Northern and Southern Africa are separated by latitude 15˚ N

• Africa is challenging because climate has changed somewhat in the past 100,000 years.  The 15˚ N latitude line divides the present day Sahara Desert from the grasslands in the west and in the east, it comes at the mouth of the Red Sea which has been proposed as a bridge area for early migration out of Africa and onto the Arabian Peninsula. It also leaves the entire Rift Valley in the Southern Africa part.